Clearance control with ceramic matrix composite rotor assembly for a gas turbine engine

ABSTRACT

A gas turbine engine includes a CMC static structure and a rotor module with a multiple of CMC airfoils, a radial growth of said rotor module matched with said CMC static structure.

BACKGROUND

The present disclosure relates to a gas turbine engine, and more particularly to Ceramic Matrix Composites (CMC) components therefor.

The turbine section of a gas turbine engine operates at elevated temperatures in a strenuous, oxidizing type of gas flow environment and is typically manufactured of high temperature superalloys. The clearance between a turbine blade and an outer static structure, known as the tip clearance, facilitates gas turbine engine performance. Tip clearances that are too large may result in leakages that are detrimental to turbine performance. Tip clearances that are too small may result in friction or wear. Maintenance of tip clearances at a suitable level facilitates efficient and robust operation.

Conventional commercial gas turbine engine tip clearance control systems typically involve active clearance control (ACC) by impinging cooler air on the outer static structure to better match the rotating hardware, but may have a weight and complexity penalty. Throttle movements on fighter aircraft too frequent to make ACC practical.

SUMMARY

A gas turbine engine according to an exemplary aspect of the present disclosure includes a CMC static structure and a rotor module with a multiple of CMC airfoils, a radial growth of the rotor module matched with the CMC static structure.

A gas turbine engine according to an exemplary aspect of the present disclosure includes a CMC case and a rotor module with a multiple of CMC airfoils, a radial growth of the rotor module matched with the CMC case.

A method of tip clearance control for a gas turbine engine according to an exemplary aspect of the present disclosure includes matching radial growth of CMC rotational structure with a radial growth of a CMC static structure to provide tip clearance control.

BRIEF DESCRIPTION OF THE DRAWINGS

Various features will become apparent to those skilled in the art from the following detailed description of the disclosed non-limiting embodiment. The drawings that accompany the detailed description can be briefly described as follows:

FIG. 1 is a schematic cross-section of a gas turbine engine;

FIG. 2 is an enlarged sectional view of a section of the gas turbine engine; and

FIG. 3 is a perspective view of a CMC Outer Air Seal.

DETAILED DESCRIPTION

FIG. 1 schematically illustrates a gas turbine engine 20. The gas turbine engine 20 is disclosed herein as a two-spool turbofan that generally incorporates a fan section 22, a compressor section 24, a combustor section 26 and a turbine section 28. Alternative engines might include an augmentor section (not shown) among other systems or features. The fan section 22 drives air along a bypass flowpath while the compressor section 24 drives air along a core flowpath for compression and communication into the combustor section 26 then expansion through the turbine section 28. Although depicted as a turbofan gas turbine engine in the disclosed non-limiting embodiment, it should be understood that the concepts described herein are not limited to use with turbofans as the teachings may be applied to other types of turbine engines.

The engine 20 generally includes a low speed spool 30 and a high speed spool 32 mounted for rotation about an engine central longitudinal axis A relative to an engine static structure 36 via several bearing systems 38. It should be understood that various bearing systems 38 at various locations may alternatively or additionally be provided.

The low speed spool 30 generally includes an inner shaft 40 that interconnects a fan 42, a low pressure compressor 44 and a low pressure turbine 46. The inner shaft 40 is connected to the fan 42 through a geared architecture 48 to drive the fan 42 at a lower speed than the low speed spool 30. The high speed spool 32 includes an outer shaft 50 that interconnects a high pressure compressor 52 and high pressure turbine 54. A combustor 56 is arranged between the high pressure compressor 52 and the high pressure turbine 54. The inner shaft 40 and the outer shaft 50 are concentric and rotate about the engine central longitudinal axis A which is collinear with their longitudinal axes.

The core airflow is compressed by the low pressure compressor 44 then the high pressure compressor 52, mixed with fuel and burned in the combustor 56, then expanded over the high pressure turbine 54 and low pressure turbine 46. The turbines 54, 46 rotationally drive the respective low speed spool 30 and high speed spool 32 in response to the expansion.

With reference to FIG. 2, the low pressure turbine 46 generally includes a turbine case 60 with a multiple of low pressure turbine stages. In the disclosed non-limiting embodiment, the turbine case 60 is manufactured of a ceramic matrix composite (CMC). It should be understood that examples of CMC material for all componentry discussed herein may include, but are not limited to, for example, S200 and SiC/SiC. Although depicted as a low pressure turbine in the disclosed embodiment, it should be understood that the concepts described herein are not limited to use with low pressure turbine as the teachings may be applied to other sections such as high pressure turbine, high pressure compressor, low pressure compressor and intermediate pressure turbine and intermediate pressure turbine of a three-spool architecture gas turbine engine.

A rotor module 62 includes a multiple (three shown) of CMC disks 64A, 64B, 64C. Each of the CMC disks 64A, 64B, 64C include a row of airfoils 66A, 66B, 66C which extend from a respective hub 68A, 68B, 68C. The rows of airfoils 66A, 66B, 66C are interspersed with CMC vane structures 70A, 70B to form a respective number of low pressure turbine stages. It should be understood that any number of stages may be provided. The case 60 and the CMC vane structures 70A, 70B are examples of static structure as defined herein in that the case 60 and the CMC vane structures 70A, 70B do not rotate about engine axis A. This is in contrast with, for example, the rotor module 62 which is an example of rotational structure as defined herein which does rotate about engine axis A.

The CMC disks 64A, 64C include arms 72A, 72C which extend from the respective hub 68A, 68C. It should be understood that a hybrid combination of materials may be utilized, for example, the respective hub 68A, 68B, 68C may alternatively be manufactured of INCO718, Waspaloy, or other metal alloy, while the airfoils 66A, 66B, 66C may be manufactured of a CMC materials It should be understood that various other materials and combinations thereof may alternatively be utilized.

An outer shroud 80A, 80B, 80C of each of the CMC disks 64A, 64B, 64C may each define at least one knife edge seal 82A, 82B, 82C which interface with the CMC Outer Air Seal (OAS) 84A, 84B, 84C. That is, the knife edge seal 82A, 82B, 82C respectively trench into the CMC Outer Air Seal (OAS) 84A, 84B, 84C. It should be understood that the CMC Outer Air Seal (OAS) 84A, 84B, 84C may include abradable materials which are relatively softer than the material of the knife edge seal 82A, 82B, 82C to facilitate trenching. The CMC OAS 84A, 84B, 84C are mounted to the case 60. In one non-limiting embodiment, the CMC OAS 84A, 84B, 84C may be full hoop structures.

The airfoils 66A, 66B, 66C of each of the CMC disks 64A, 64B, 64C have a relatively low centrifugal pull which lessens the relative radial growth of the low pressure turbine rotor module 62. Thermal growth of the CMC airfoils 66A, 66B, 66C is also relatively less than conventional alloy materials. The radial growth of the CMC airfoils 66A, 66B, 66C is matched to the growth of the CMC turbine case 60. That is, the radial growth of that rotational structure is matched with the static structure to inherently provide clearance control. “Matched” as defined herein may be considered as a generally equivalent—between rate of thermal growth of the static structure and rate of thermal growth/centrifugal pull growth of the rotational structure such that the airfoils 66A, 66B, 66C maintain tip clearances at a suitable level to facilitate efficient and robust operation during flight operations.

In another non-limiting embodiment, an interface 86A, 86B, 86C may alternatively or additionally be utilized to mount the CMC OAS 84A, 84B, 84C to the turbine case 60 which may alternatively be manufactured of a metallic alloy material to permit relative radial growth therebetween. It should be understood that the interface 86A, 86B, 86C may also be utilized with a turbine case 60 which is manufactured of a CMC material to provide additional radial match capability.

The interface 86A, 86B, 86C may be a splined interface (also illustrated in FIG. 3) for attachment to the case 60 which includes a corresponding static support structure 88A, 88B, 88C which extend radially inward toward the engine axis A. The static support structure 88A, 88B, 88C receive the interface 86A, 86B, 86C to permit a floating ring structure to further match radial expansion and contraction due to thermal variances yet maintains the concentricity of the CMC OAS 84A, 84B, 84C about engine axis A.

Strategic utilization of CMC materials with their low thermal expansion characteristics permits the radial growth of the rotational structure and stationary structure to be matched so as to provide a controlled tip clearance without the weight and complexity of a conventional clearance control system.

It should be understood that like reference numerals identify corresponding or similar elements throughout the several drawings. It should also be understood that although a particular component arrangement is disclosed in the illustrated embodiment, other arrangements will benefit herefrom.

Although particular step sequences are shown, described, and claimed, it should be understood that steps may be performed in any order, separated or combined unless otherwise indicated and will still benefit from the present disclosure.

The foregoing description is exemplary rather than defined by the limitations within. Various non-limiting embodiments are disclosed herein, however, one of ordinary skill in the art would recognize that various modifications and variations in light of the above teachings will fall within the scope of the appended claims. It is therefore to be understood that within the scope of the appended claims, the disclosure may be practiced other than as specifically described. For that reason the appended claims should be studied to determine true scope and content. 

1. A gas turbine engine comprising: a CMC static structure; and a rotor module with a multiple of CMC airfoils, a radial growth of said rotor module matched with said CMC static structure.
 2. The gas turbine engine as recited in claim 1, wherein said CMC static structure is a CMC Outer Air Seal.
 3. The gas turbine engine as recited in claim 2, further comprising an abradable material mounted to said CMC Outer Air Seal.
 4. The gas turbine engine as recited in claim 2, wherein said CMC Outer Air Seal is mounted to a CMC case.
 5. The gas turbine engine as recited in claim 2, wherein said CMC Outer Air Seal is mounted to a metallic alloy case.
 6. The gas turbine engine as recited in claim 1, wherein said CMC static structure is a CMC turbine case.
 7. The gas turbine engine as recited in claim 1, wherein said CMC static structure is a CMC compressor case.
 8. A gas turbine engine comprising: a CMC case; and a rotor module with a multiple of CMC airfoils, a radial growth of said rotor module matched with said CMC case.
 9. The gas turbine engine as recited in claim 8, further comprising a CMC Outer Air Seal mounted to said CMC case.
 10. The gas turbine engine as recited in claim 8, further comprising at least one knife edge seal which extends from each of said multiple of CMC airfoils, said at least one knife edge seal engaged with said CMC Outer Air Seal.
 11. The gas turbine engine as recited in claim 8, further comprising an outer shroud defined about said multiple of CMC airfoils.
 12. The gas turbine engine as recited in claim 8, wherein said rotor module is defined about an engine longitude axis.
 13. The gas turbine engine as recited in claim 8, wherein said rotor module is a Low Pressure Turbine rotor module.
 14. The gas turbine engine as recited in claim 8, wherein said rotor module is a High Pressure Turbine rotor module.
 15. The gas turbine engine as recited in claim 8, wherein said rotor module is a compressor rotor module.
 16. A method of tip clearance control for a gas turbine engine comprising: matching radial growth of CMC rotational structure with a radial growth of a CMC static structure to provide tip clearance control.
 17. The method as recited in claim 16, wherein the CMC rotational structure includes a rotor module with a multiple of CMC airfoils.
 18. The method as recited in claim 16, wherein the CMC static structure includes a case structure. 